The present invention relates to fuel system valves, and particularly to a tank venting control assembly for regulating the flow of fuel vapor and air through a venting outlet provided in a fuel tank having a separate filler neck. More particularly, the present invention relates to a vehicle fuel vapor control valve which performs pressure-relief and vacuum-relief functions and also maintains a predetermined head pressure in the fuel tank during stationary refueling while relieving some fuel vapor pressure in the fuel tank when the vehicle is in motion.
Vehicle fuel systems are known to include tank pressure control valves configured to provide tank pressure relief and tank vacuum relief and to mount on either fuel tanks or filler necks. See, for example, U.S. Pat. No. 5,234,013 to Roetker et al., U.S. Pat. No. 4,498,493 to Harris, and U.S. Pat. Nos. 4,953,583 and 5,065,782 to Szlaga.
Although fuel pump nozzles are known to include sensor means for shutting off the flow of fuel from the nozzle when the fuel tank is nearly filled, it has been observed that users frequently manually override or bypass such fill-limiting sensors by continuing to pump fuel after the pump nozzle has automatically shut off several times. It will be appreciated that such unauthorized refueling practices can result in overfilling the fuel tank which can effectively reduce the fuel vapor expansion capacity available within the filled fuel tank.
It is also known to provide fuel vapor control valves for regulating tank pressure to prevent overfilling of the fuel tank during refueling. See, for example, U.S. Pat. No. 4,760,858 to Szlaga. Such a fuel vapor control valve includes a movable head valve for maintaining a head pressure within the fuel tank which exceeds the maximum head pressure that can develop in the filler neck due to filling the filler neck with fuel during refueling. Such a fuel vapor control valve aids in preventing fuel pump operators from overfilling fuel tanks by providing a pressurized fuel vapor barrier within the fuel tank that acts to block the introduction of liquid fuel into the fuel tank in excess of a predetermined fuel capacity during refueling. Such a fuel vapor control valve is adapted to vibrate to allow the release of fuel vapor during vehicle transit to increase the flow of fuel vapor to a fuel vapor treatment site and/or the atmosphere, thereby enhancing engine performance.
What is needed is a fuel vapor control valve for preventing tank overfilling during refueling and for relieving vacuum conditions that develop in a tank. Consumers would welcome a fuel vapor control valve that was also operable to vent minimal or residual tank pressure during motion of a vehicle carrying the tank and/or excessive tank pressure whether the vehicle is in motion or stationary.
According to the present invention an apparatus is provided for controlling venting of fuel vapor through an aperture in a fuel tank. The apparatus comprises a housing mounted in the aperture and a valve moveable in the housing. The housing is formed to include an outlet and defines a vent path for fuel vapor between the fuel tank and the outlet. The valve is moveable in the housing between the blocking position blocking flow of fuel vapor between the fuel tank and the outlet along the vent path and a venting position allowing flow of fuel vapor between the fuel tank and the outlet along the vent path. A spring biases the valve toward its blocking position.
The apparatus also comprises means for using fuel vapor from the fuel tank to move the valve against the spring towards its venting position. The using means includes a venting control chamber receiving fuel vapor from the fuel tank and a conduit communicating fuel vapor from the fuel tank to the venting control chamber. A ball is movably positioned in the venting control chamber to selectively interrupt the flow of fuel vapor through the conduit. The conduit has a first portion and a second portion moveable relative to the first portion to define an intermediate portion.
The apparatus further comprises a flexible partition extending between the valve and the first portion of the conduit to provide a barrier to prevent fuel vapor venting through the vent path from entering the intermediate portion. The flexible partition is deformable to maintain the barrier when the valve moves away from its blocking position towards its venting position.
In preferred embodiments, the using means includes a valve actuator for using fuel vapor from the fuel tank to urge the valve toward its venting position. The valve actuator includes a diaphragm covering the venting control chamber, and the diaphragm has an edge arranged to define an aperture. The conduit includes a stem appended to the edge of the diaphragm and arranged to define a flow channel so that the venting control chamber is in fluid communication with the flow channel through the aperture.
The ball is movably contained by a cage appended to the diaphragm and is positioned to interrupt the flow of fuel vapor through the conduit by sealingly engaging the edge of the diaphragm. The ball has a predetermined weight sufficient to interrupt the flow of fuel vapor through the aperture of the diaphragm so long as the vehicle remains substantially stationary and the tank pressure does not exceed a predetermined pressure set-point.
In use, the pressure-relief valve operates to vent excessive tank pressure to a fuel vapor treatment canister or other destination through the venting outlet formed in the housing. The pressure-relief valve operates to provide three levels of pressure relief depending upon the pressure of the fuel vapor in the fuel tank and whether the vehicle is stationary or in motion.
At the lowest level of pressure relief, the ball-type head valve operates during motion of a vehicle carrying the fuel tank to vent residual tank pressure to the canister even though tank pressure does not exceed the level required to activate the pressure-relief valve. This residual pressure is normally the pressure that is left in the tank after refueling.
During refueling, the ball-type head valve closes the venting outlet to cause a pressurized fuel vapor barrier to develop within the fuel tank. This barrier acts to block the introduction of liquid fuel into the fuel tank through the filler neck once the fuel tank is filled to its rated capacity. However, once refueling is completed and this barrier is no longer needed the ball-type head valve moves in response to vehicle movement to cause a vent passage in the housing chamber to open and vent some of the residual tank pressure through the venting outlet to the canister.
Advantageously, the ball normally resides in a sealing position on a conic surface having a pressure signal supply orifice in its trough. The ball seeks this sealing position when the valve is stationary. By plugging the orifice to halt the pressure signal to the top of the diaphragm, the valve moves to the blocking position. Once the valve is in the blocking position, the flow of fuel vapor between the fuel tank and the outlet ceases permitting a controlled fill of the fuel system and a full level shut off using a float valve or stand pipe controlled vent. The valve resumes normal ventilation when the assembly is accelerated agitating the ball and moving the ball from its seat thereby allowing the pressure signal to open the valve.
At the intermediate level of pressure relief, the ball-type head valve moves in response to vehicle movement to cause a vent passageway in the housing to open. The open passageway allows fuel vapor to accumulate and if the tank pressure is above a first predetermined pressure set-point, the fuel vapor will activate the valve actuator. Once activated, the valve actuator will move the valve to the venting position allowing the flow of fuel vapor from the fuel tank to the outlet along the vent path.
At the highest level of pressure relief when the vehicle is stationary, the ball-type head valve initially interrupts the flow of fuel vapor. The passageway will remain closed until the fuel vapor pressure in the fuel tank reaches a second predetermined pressure set-point at which the fuel vapor will unseat the sealing ball. Once the sealing ball is unseated, the open passageway allows fuel vapor to accumulate and if the second predetermined pressure set-point is above the first predetermined pressure set-point, the fuel vapor will activate the valve actuator. Once activated, the valve actuator will move the valve to the venting position allowing the flow of fuel vapor from the fuel tank to the outlet along the vent path.